Frame transmitting method and frame receiving method

ABSTRACT

A method of transmitting a frame by a device in a wireless communication network is provided. The device generates a first symbol having a first subcarrier spacing where a symbol duration of the first symbol, excluding a guard interval, has a first length. The device generates a second symbol having a second subcarrier spacing narrower than the first subcarrier spacing wherein a symbol duration of the second symbol, excluding a guard interval, has a second length that is twice the first length. The device transmits a frame including the first symbol and the second symbol.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of PCT/US15/47304, filed Aug. 27,2015, which claims priority to and the benefit of Korean PatentApplication No. 10-2014-0113391, filed on Aug. 28, 2014, in the KoreanIntellectual Property Office, the entire contents of which areincorporated herein by reference.

BACKGROUND

(a) Field

The described technology relates generally to a frame transmittingmethod and a frame receiving method. More particularly, the describedtechnology generally relates to a frame transmitting method and a framereceiving method in a wireless local area network (WLAN).

(b) Description of the Related Art

A WLAN is being standardized by the IEEE (Institute of Electrical andElectronics Engineers) Part 11 under the name of “Wireless LAN MediumAccess Control (MAC) and Physical Layer (PHY) Specifications.”

After an original standard was published in 1999, new version standardsare continuously published by amendments. The IEEE standard 802.11a(IEEE Std 802.11a-1999) supporting 2.4 GHz band was published in 1999,and the IEEE standard 802.11g (IEEE Std 802.11g-2003) supporting 5 GHzband was published in 2003. These standards are called legacy.Subsequently, the IEEE standard 802.11n (IEEE Std 802.11n-2009) forenhancements for higher throughput (HT) was published in 2009, and theIEEE standard 802.11ac (IEEE 802.11ac-2013) for enhancements for veryhigh throughput (VHT) was published in 2013.

Recently, the WLAN has been considered for use as a network for coveringa wide area in an outdoor environment. Accordingly, a high efficiency(HE) WLAN suitable for the outdoor environment is being developed by theIEEE 802.11ax task group. In order to be suitable for the outdoorenvironment, a length of a guard interval provided by a cyclic prefixmay be lengthened, so a length of a symbol may be lengthened.Accordingly, the length of the symbol in the HE WLAN or a subsequentWLAN may be lengthened.

SUMMARY OF THE INVENTION

An embodiment of the present disclosure provides a frame transmittingmethod and a frame receiving method for increasing a length of a symbol.

According to an embodiment, a method of transmitting a frame is providedby a device in a wireless communication network. The method includesgenerating a first symbol having a first subcarrier spacing, generatinga second symbol having a second subcarrier spacing narrower than thefirst subcarrier spacing, and transmitting a frame including the firstsymbol and the second symbol. A symbol duration of the first symbol,excluding a guard interval, has a first length, and a symbol duration ofthe second symbol, excluding a guard interval, has a second length thatis twice the first length.

The first length may be 3.2 μs and the second length may be 6.4 μs.

Generating the second symbol may include performing an inverse Fouriertransform by using only even-numbered subcarriers among the plurality ofsubcarriers, and using only one period of two periods that are output bythe inverse Fourier transform.

The method may further include generating a third symbol, a symbolduration of the third symbol, excluding a guard interval, has a thirdlength that is twice the second length. The frame may further includethe third symbol.

The third length may be 12.8 μs.

The frame may include a legacy preamble part, a HE (high efficiency)long training field that follows the legacy preamble part and is adaptedfor use in channel estimation, and a data field. The legacy preamblepart may include the first symbol, the HE long training field mayinclude the second symbol, and the data field may include the thirdsymbol.

When a basic bandwidth of the frame is divided into a plurality ofsubbands, the data field may be encoded per each subband andtransmitted, and the data field transmitted on subband may include datafor a receiving device allocated to the subband.

The frame may further include a first HE signal field and a second HEsignal field that both follow the legacy preamble part. The second HEsignal field may be encoded per the basic bandwidth and transmitted, andmay include allocation information of the subbands.

The second HE signal field may further include information on devicesthat receive the frame on each subband.

The basic bandwidth may be 20 MHz.

The legacy preamble part may further include a legacy signal field, andtwo symbols that immediately follow the legacy signal field may bemodulated by using BPSK (binary phase shift keying) modulation.

According to yet another embodiment, a method of receiving a frame isprovided by a device in a wireless communication network. The methodincludes detecting in a frame a first symbol having a first subcarrierspacing and a second symbol having a second subcarrier spacing narrowerthan the first subcarrier spacing, and processing the first symbol andthe second symbol in the frame. A symbol duration of the first symbol,excluding a guard interval, has a first length and a symbol duration ofthe second symbol, excluding a guard interval, has a second length thatis twice the first length.

Processing the first symbol and the second symbol may include performinga Fourier transform on the first symbol by using a fast Fouriertransform (FFT) having a first size, and performing a Fourier transformon the second symbol by using an FFT having a second size different fromthe first size.

The second size may be four times the first size. Performing the Fouriertransform on the second symbol may include generating an interval havingtwo periods by copying an interval excluding a guard interval from thesecond symbol, and performing the Fourier transform on the intervalhaving the two periods.

The first length may be 3.2 μs and the second length may be 6.4 μs.

The frame may further include a third symbol, a symbol duration of thethird symbol, excluding a guard interval, has a third length that istwice the second length.

The frame may include a legacy preamble part, a long training field thatfollows the legacy preamble part and is adapted for use in channelestimation, and a data field. The legacy preamble part may include thefirst symbol, the long training field may include the second symbol, andthe data field may include the third symbol.

The frame may further include a first HE signal field and a second HEsignal field that both follow the legacy preamble part. When a basicbandwidth of the frame is divided into a plurality of subbands, the datafield may be encoded per a subband unit and transmitted on a subband ofthe plurality of subbands. Further, the second HE signal field may beencoded per the basic bandwidth and transmitted, and may includeallocation information for the subbands.

The second HE signal field may further include information on devicesthat receive the frame on each subband.

The legacy preamble part may further include a legacy signal field, andtwo symbols that immediately follow the legacy signal field may bemodulated by using BPSK modulation.

According to still another embodiment, an apparatus for transmitting aframe is provided in a wireless communication network. The apparatusincludes a processor and a transceiver. The processor generates a firstsymbol having a first subcarrier spacing and generates a second symbolhaving a second subcarrier spacing narrower than the first subcarrierspacing. The transceiver transmits a frame including the first symboland the second symbol. A symbol duration of the first symbol, excludinga guard interval, has a first length, and a symbol duration of thesecond symbol, excluding a guard interval, has a second length that istwice the first length.

According to a further embodiment, an apparatus for receiving a frame isprovided in a wireless communication network. The apparatus includes aprocessor and a transceiver. The transceiver detects in a frame a firstsymbol having a first subcarrier spacing and a second symbol havingsecond subcarrier spacing narrower than the first subcarrier spacing.The processor processes the first symbol and the second symbol in theframe. A symbol duration of the first symbol, excluding a guardinterval, has a first length and a symbol duration of the second symbol,excluding a guard interval, has a second length that is twice the firstlength.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of a WLAN device according to anembodiment.

FIG. 2 is a schematic block diagram of a transmitting signal processorin an embodiment suitable for use in a WLAN.

FIG. 3 is a schematic block diagram of a receiving signal processingunit in an embodiment suitable for use in the WLAN.

FIG. 4 illustrates Inter-Frame Space (IFS) relationships.

FIG. 5 is a schematic diagram illustrating a CSMA/CA based frametransmission procedure for avoiding collision between frames in achannel.

FIG. 6 shows an example of a wireless communication network according toan embodiment.

FIG. 7 schematically shows an example of a frame format of a wirelesscommunication network according to an embodiment.

FIG. 8 and FIG. 9 illustrate a 64-point Fast Fourier Transform (FFT)symbol in a wireless communication network according to variousembodiments.

FIG. 10, FIG. 11, FIG. 12, and FIG. 13 illustrate a 256-point FFT symbolin a wireless communication network according to various embodiments.

FIG. 14 illustrates a general subcarrier allocation in a wirelesscommunication network according to an embodiment.

FIG. 15 illustrates a subcarrier allocation of a High Efficiency (HE)long training field (LTF) in a wireless communication network accordingto an embodiment.

FIG. 16 illustrates generation of a HE long training field in a wirelesscommunication network according to an embodiment.

FIG. 17, FIG. 18, FIG. 21, and FIG. 22 each schematically illustrates aframe format in a wireless communication network according to variousembodiments.

FIG. 19 and FIG. 20 show examples of subcarrier allocation in a frameformat shown in FIG. 17 according to an embodiment.

FIG. 23 and FIG. 24 schematically illustrate a frame format in awireless communication network according to various embodiments.

FIG. 25 illustrates an auto-detection method of a legacy frame accordingto an embodiment.

FIG. 26 illustrates an auto-detection method of an HT frame according toan embodiment.

FIG. 27 illustrates an auto-detection method of a VHT frame according toan embodiment.

FIG. 28, FIG. 29, and FIG. 30 each illustrates an auto-detection methodof a HE frame in a wireless communication network according to anembodiment.

FIG. 31 is a flowchart illustrating a frame transmitting method in awireless communication network according to an embodiment.

FIG. 32 is a flowchart illustrating a frame receiving method in awireless communication network according to an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following detailed description, only certain embodiments havebeen shown and described, simply by way of illustration. As thoseskilled in the art would realize, the described embodiments may bemodified in various different ways, all without departing from thespirit or scope of the present disclosure. Accordingly, the drawings anddescription are to be regarded as illustrative in nature and notrestrictive. Like reference numerals designate like elements throughoutthe specification.

In a wireless local area network (WLAN), a basic service set (BSS)includes a plurality of WLAN devices. The WLAN device may include amedium access control (MAC) layer and a physical (PHY) layer accordingto the IEEE (Institute of Electrical and Electronics Engineers) standard802.11. The plurality of WLAN devices may include a WLAN device that isan access point and the other WLAN devices that are non-AP stations(non-AP STAs). Alternatively, all of the plurality of WLAN devices maybe non-AP STAs in ad-hoc networking. In general, the AP STA and thenon-AP STAs may be collectively called STAs. However, for ease ofdescription, herein, only the non-AP STAs are referred to as the STAs.

FIG. 1 is a schematic block diagram of a WLAN device according to anembodiment.

Referring to FIG. 1, the WLAN device 1 includes a baseband processor 10,a radio frequency (RF) transceiver 20, an antenna unit 30, a memory 40including non-transitory computer-readable media, an input interfaceunit 50, an output interface unit 60, and a bus 70.

The baseband processor 10 performs baseband signal processing, andincludes a MAC processor 11 and a PHY processor 15.

In one embodiment, the MAC processor 11 may include a MAC softwareprocessing unit 12 and a MAC hardware processing unit 13. The memory 40may store software (hereinafter referred to as “MAC software”) includingat least some functions of the MAC layer. The MAC software processingunit 12 executes the MAC software to implement some functions of the MAClayer, and the MAC hardware processing unit 13 may implement remainingfunctions of the MAC layer as hardware (hereinafter referred to “MAChardware”). However, embodiments of the MAC processor 11 are not limitedto this.

The PHY processor 15 includes a transmitting (Tx) signal processing unit100 and a receiving (Rx) signal processing unit 200.

The baseband processor 10, the memory 40, the input interface unit 50,and the output interface unit 60 may communicate with each other via thebus 70.

The RF transceiver 20 includes an RF transmitter 21 and an RF receiver22.

The memory 40 may further store an operating system and applications.The input interface unit 50 receives information from a user, and theoutput interface unit 60 outputs information to the user.

The antenna unit 30 includes one or more antennas. When multiple-inputmultiple-output (MIMO) or multi-user MIMO (MU-MIMO) is used, the antennaunit 30 may include a plurality of antennas.

FIG. 2 is a schematic block diagram of a transmitting signal processor100 according to an embodiment suitable for use in a WLAN.

Referring to FIG. 2, a transmitting signal processing unit 100 includesan encoder 110, an interleaver 120, a mapper 130, an inverse Fouriertransformer (IFT) 140, and a guard interval (GI) inserter 150.

The encoder 110 encodes input data. For example, the encoder 100 may bea forward error correction (FEC) encoder. The FEC encoder may include abinary convolutional code (BCC) encoder followed by a puncturing device,or may include a low-density parity-check (LDPC) encoder.

The transmitting signal processing unit 100 may further include ascrambler for scrambling the input data before the encoding to reducethe probability of long sequences of 0s or 1s. If BCC encoding is usedin the encoder, the transmitting signal processing unit 100 may furtherinclude an encoder parser for demultiplexing the scrambled bits among aplurality of BCC encoders. If LDPC encoding is used in the encoder, thetransmitting signal processing unit 100 may not use the encoder parser.

The interleaver 120 interleaves the bits of each stream output from theencoder to change an order of bits. Interleaving may be applied onlywhen BCC encoding is used. The mapper 130 maps the sequence of bitsoutput from the interleaver to constellation points. If the LDPCencoding is used in the encoder, the mapper 130 may further perform LDPCtone mapping besides the constellation mapping.

When the MIMO or the MU-MIMO is used, the transmitting signal processingunit 100 may use a plurality of interleavers 120 and a plurality ofmappers 130 corresponding to a number of spatial streams N_(SS). In thiscase, the transmitting signal processing unit 100 may further include astream parser for dividing outputs of the BCC encoders or the LDPCencoder into blocks that are sent to different interleavers 120 ormappers 130. The transmitting signal processing unit 100 may furtherinclude a space-time block code (STBC) encoder for spreading theconstellation points from the N_(SS) spatial streams into N_(STS)space-time streams and a spatial mapper for mapping the space-timestreams to transmit chains. The spatial mapper may use direct mapping,spatial expansion, or beamforming

The IFT 140 converts a block of the constellation points output from themapper 130 or the spatial mapper to a time domain block (i.e., a symbol)by using an inverse discrete Fourier transform (IDFT) or an inverse fastFourier transform (IFFT). If the STBC encoder and the spatial mapper areused, the inverse Fourier transformer 140 may be provided for eachtransmit chain.

When the MIMO or the MU-MIMO is used, the transmitting signal processingunit 100 may insert cyclic shift diversities (CSDs) to preventunintentional beamforming. The CSD insertion may occur before or afterthe inverse Fourier transform. The CSD may be specified per transmitchain or may be specified per space-time stream. Alternatively, the CSDmay be applied as a part of the spatial mapper.

When the MU-MIMO is used, some blocks before the spatial mapper may beprovided for each user.

The GI inserter 150 prepends a guard interval (GI) to the symbol. Thetransmitting signal processing unit 100 may optionally perform windowingto smooth edges of each symbol after inserting the GI. The RFtransmitter 21 converts the symbols into an RF signal and transmits theRF signal via the antenna unit 30. When the MIMO or the MU-MIMO is used,the GI inserter 150 and the RF transmitter 21 may be provided for eachtransmit chain.

FIG. 3 is a schematic block diagram of a receiving signal processingunit 200 according to an embodiment suitable for use in the WLAN.

Referring to FIG. 3, a receiving signal processing unit 200 includes aGI remover 220, a Fourier transformer (FT) 230, a demapper 240, adeinterleaver 250, and a decoder 260.

An RF receiver 22 receives an RF signal via the antenna unit 30 andconverts the RF signal into a symbol. The GI remover 220 removes the GIfrom the symbol. When the MIMO or the MU-MIMO is used, the RF receiver22 and the GI remover 220 may be provided for each receive chain.

The FT 230 converts the symbol (i.e., the time domain block) into ablock of the constellation points by using a discrete Fourier transform(DFT) or a fast Fourier transform (FFT). The Fourier transformer 230 maybe provided for each receive chain.

When the MIMO or the MU-MIMO is used, the receiving signal processingunit 200 may include a spatial demapper for converting the Fouriertransformed received symbols to constellation points of the space-timestreams, and an STBC decoder for despreading the constellation pointsfrom the space-time streams into the spatial streams.

The demapper 240 demaps the constellation points output from the Fouriertransformer 230 or the STBC decoder to the bit streams. If the LDPCencoding is used, the demapper 240 may further perform LDPC tonedemapping before the constellation demapping. The deinterleaver 250deinterleaves the bits of each stream output from the demapper 240.Deinterleaving may be applied only when BCC encoding is used.

When the MIMO or the MU-MIMO is used, the receiving signal processingunit 200 may use a plurality of demappers 240 and a plurality ofdeinterleavers 250 corresponding to the number of spatial streams. Inthis case, the receiving signal processing unit 200 may further includea stream deparser for combining the streams output from thedeinterleavers 250.

The decoder 260 decodes the streams output from the deinterleaver 250 orthe stream deparser. For example, the decoder 100 may be an FEC decoder.The FEC decoder may include a BCC decoder or an LDPC decoder. Thereceiving signal processing unit 200 may further include a descramblerfor descrambling the decoded data. If BCC decoding is used in thedecoder, the receiving signal processing unit 200 may further include anencoder deparser for multiplexing the data decoded by a plurality of BCCdecoders. If LDPC decoding is used in the decoder, the receiving signalprocessing unit 100 may not use the encoder deparser.

FIG. 4 illustrates interframe space (IFS) relationships.

A data frame, a control frame, or a management frame may be exchangedbetween WLAN devices.

The data frame is used for transmission of data forwarded to a higherlayer. The WLAN device transmits the data frame after performing backoffif a distributed coordination function IFS (DIFS) has elapsed from atime when the medium has been idle. The management frame is used forexchanging management information which is not forwarded to the higherlayer. Subtype frames of the management frame include a beacon frame, anassociation request/response frame, a probe request/response frame, andan authentication request/response frame. The control frame is used forcontrolling access to the medium. Subtype frames of the control frameinclude a request to send (RTS) frame, a clear to send (CTS) frame, andan acknowledgement (ACK) frame. When the control frame is not a responseframe of a previous frame, the WLAN device transmits the control frameafter performing backoff when the DIFS has elapsed. When the controlframe is the response frame of the previous frame, the WLAN devicetransmits the control frame without performing backoff when a short IFS(SIFS) has elapsed. The type and subtype of a frame may be identified bya type field and a subtype field in a frame control field.

On the other hand, a Quality of Service (QoS) STA may transmit the frameafter performing backoff when an arbitration IFS (AIFS) for accesscategory (AC), i.e., AIFS[AC], has elapsed. In this case, the dataframe, the management frame, or the control frame which is not theresponse frame may use the AIFS[AC].

FIG. 5 is a schematic diagram illustrating a CSMA (carrier sensemultiple access)/CA (collision avoidance) based frame transmissionprocedure for avoiding collision between frames in a channel.

Referring to FIG. 5, STA1 is a transmit WLAN device for transmittingdata, STA2 is a receive WLAN device for receiving the data, and STA3 isa third WLAN device which may be located at an area where a frametransmitted from the STA1 and/or a frame transmitted from the STA2 canbe received by the third WLAN device STA3.

The STA1 may determine whether the channel is busy by carrier sensing.The STA1 may determine the channel occupation based on an energy levelon the channel or correlation of signals in the channel, or maydetermine the channel occupation by using a network allocation vector(NAV) timer.

When it is determined that the channel is not in use by other devicesduring DIFS (that is, that the channel is idle), the STA1 may transmitan RTS frame to the STA2 after performing backoff. Upon receiving theRTS frame, the STA2 may transmit a CTS frame as a response of the CTSframe after a SIFS.

When the STA3 receives the RTS frame, it may set the NAV timer for atransmission duration of subsequently transmitted frames by usingduration information included in the RTS frame. For example, the NAVtimer may be set for a duration of SIFS+CTS frame duration+SIFS+dataframe duration+SIFS+ACK frame duration. When the STA3 receives the CTSframe, it may set the NAV timer for a transmission duration ofsubsequently transmitted frames by using duration information includedin the CTS frame. For example, the NAV timer may be set for a durationof SIFS+data frame duration+SIFS+ACK frame duration. Upon receiving anew frame before the NAV timer expires, the STA3 may update the NAVtimer by using duration information included in the new frame. The STA3does not attempt to access the channel until the NAV timer expires.

When the STA1 receives the CTS frame from the STA2, it may transmit adata frame to the STA2 after a SIFS elapses from a time when the CTSframe has been completely received. Upon successfully receiving the dataframe, the STA2 may transmit an ACK frame as a response of the dataframe after a SIFS elapses.

When the NAV timer expires, the STA3 may determine whether the channelis busy by the carrier sensing. Upon determining that the channel is notin use by the other devices during DIFS after the NAV timer has expired,the STA3 may attempt the channel access after a contention windowaccording to random backoff elapses.

Now, a frame transmitting method and a frame receiving method in awireless communication network according to an embodiment is describedwith reference to the drawings. A wireless communication networkaccording to an embodiment may be a WLAN. Particularly, the wirelesscommunication network according to an embodiment may be a highefficiency (HE) WLAN developed by the IEEE 802.11ax task group.Hereinafter, it is assumed for convenience that the wirelesscommunication network according to an embodiment is a HE WLAN.

FIG. 6 shows an example of a wireless communication network according toan embodiment, and FIG. 7 schematically shows an example of a frameformat of a wireless communication network according to an embodiment.

Referring to FIG. 6, a basic service set (BSS) 600 includes a pluralityof WLAN devices. The plurality of WLAN devices include an access point(AP) 610 and a non-AP station, i.e., a station 620

The AP 610 and the station 620 are devices supporting a wirelesscommunication network according to an embodiment, e.g., a HE WLAN.Hereinafter, such a device is referred to as a HE device. Further, an APsupporting the HE WLAN is referred to as a HE-AP, and a stationsupporting the HE WLAN is referred to as a HE-STA.

The BSS 600 may further include a previous version device. The previousversion device may be, for example, a device (hereinafter referred to asa “legacy device”) supporting the IEEE standard 802.11a or 802.11g (IEEEStd 802.11a-1999 or IEEE Std 802.11g-2003), a device (hereinafterreferred to as an “HT device”) supporting the IEEE standard 802.11n(IEEE Std 802.11n-2009) for enhancements for higher throughput (HT), ora device (hereinafter referred to as a “VHT device”) supporting the IEEEstandard 802.11ac (IEEE Std 802.11ac-2013) for enhancements for veryhigh throughput (VHT).

Referring to FIG. 7, a frame according to an embodiment includes alegacy preamble part 710 and a part supporting a wireless communicationnetwork according to an embodiment, for example a HE compatible part720. The frame shown in FIG. 7 may be a physical layer (PHY) frame, forexample a physical layer convergence procedure (PLCP) frame. Further,the frame shown in FIG. 7 may be a downlink frame transmitted by the APor an uplink frame transmitted by the station.

The legacy preamble part 710 includes a legacy preamble for backwardcompatibility with previous version WLAN devices. The legacy preambleincludes a legacy short training field (L-STF), a legacy long trainingfield (L-LTF), and a legacy signal field (L-SIG). The L-STF may be usedfor initial synchronization, signal detection, and automatic gaincontrol. The L-LTF may be used for fine frequency synchronization andchannel estimation. The L-SIG may include signaling information such aslength information representing a length of the entire frame.

The HE compatible part 720 includes a HE preamble and a data field. Thedata field includes data to be transmitted, and the data may correspondto a MAC frame.

The HE preamble includes a HE signal field (HE-SIG-A) following theL-SIG and carrying signaling information for a HE device. The lengthinformation of the L-SIG and the signaling information of the HE-SIG-Amay be decoded based on the channel information estimated by the L-LTF.The HE preamble may further include an additional HE signal field(HE-SIG-B).

The HE preamble may further include a HE long training field (HE-LTF).The HE-LTF may be used for channel estimation of the HE compatible part720. The HE-LTF may include a plurality of HE-LTFs. Each of the HE-LTFsmay correspond to one symbol, for example, an orthogonal frequencydivision multiplexing (OFDM) symbol. The data, i.e., the MAC frame partof the data field, may be decoded using the channel informationestimated using the HE-LTF.

In some embodiments, the HE-LTF may be used for multiple input multipleoutput (MIMO) channel estimation. The number of HE-LTFs may bedetermined based on the number of antennas used for the MIMOtransmission, i.e., the number of space-time streams.

The HE preamble may further include a HE short training field (HE-STF).The HE-STF may be used for automatic gain control of the HE compatiblepart 720 and may correspond to one symbol. The HE-STF may precede theHE-LTF.

A second HE signal field (HE-SIG-B) (not shown) may follow the HE-LTF,or may follow the HE-SIG-A.

In some embodiments, a basic bandwidth may be divided into a pluralityof subbands to enhance frequency usage efficiency in the HE WLAN. Forthis, the HE WLAN may use a transmission scheme such as an orthogonalfrequency-division multiple access (OFDMA) scheme. Further, the HE WLANmay be considered for use in an outdoor environment. However, when aguard interval (GI) of the previous WLAN, that is, a WLAN based on aprevious WLAN standard, is used in the outdoor environment, theperformance can be degraded because a length of the GI, for example 800nsec, is short. Accordingly, in an embodiment, the GI may be lengthenedsuch that a symbol (i.e., an OFDM symbol) may be lengthened.

Hereinafter, such an embodiment is described with reference to FIG. 8 toFIG. 15.

FIG. 8 and FIG. 9 illustrate a 64 point FFT symbol in a wirelesscommunication network according to various embodiments, and FIG. 10,FIG. 11, FIG. 12, and FIG. 13 illustrate a 256 point FFT symbol in awireless communication network according to various embodiments.

In an embodiment, subcarrier spacing is shortened to increase a lengthof an OFDM symbol. An FFT having a larger size than an FFT used in theprevious WLAN (i.e., a legacy WLAN, an HT WLAN, or a VHT WLAN) is used.

In some embodiments, the subcarrier spacing that is applied to symbolsof a legacy preamble part (710 of FIG. 7) and a HE-SIG-A is equal to thesubcarrier spacing of the previous WLAN, for backward compatibility withthe previous WLAN standard. That is, an FFT having the same size as theprevious WLAN is used. The FFT used in the previous WLAN may be a 64point FFT on a 20 MHz basic bandwidth, wherein the subcarrier spacingused in the previous WLAN is 312.5 kHz(=20 MHz/64). Accordingly, 64subcarriers per symbol can be used on the 20 MHz basic bandwidth. Asshown in FIG. 8 and FIG. 9, each symbol of the legacy preamble part andthe HE-SIG-A may include a data interval corresponding to an FFT periodwith 3.2 μs length and a GI that is prepended to the data interval andhas the length of 0.4 μs or 0.8 μs. In an embodiment, the GI may beformed using a cyclic prefix (CP) of the data interval. In this case, a0.4 μs GI may be called ⅛ CP since it is formed by the CP correspondingto ⅛ of 3.2 μs length. A 0.8 μs GI may be called ¼ CP since it is formedby the CP corresponding to ¼ of 3.2 μs length.

In a wireless communication network according to an embodiment,subcarrier spacing narrower than 312.5 kHz is applied to some fieldsincluding a data field in a HE compatible part (720 of FIG. 7). That is,an FFT that has a size larger than 64 FFT on the 20 MHz basic bandwidthis applied to some fields of the HE compatible part 720. For example, aninverse Fourier transformer (140 of FIG. 2) of a transmitting device mayuse the FFT having a size larger than a 64 point FFT when performing anIFFT, and a Fourier transformer (230 of FIG. 3) of a receiving devicemay use a FFT having a size larger than the 64 point FFT when performinga FFT.

In some embodiments, as shown in FIG. 10, FIG. 11, FIG. 12, and FIG. 13,a subcarrier spacing (i.e., 78.125 kHz) that corresponds to ¼ of thesubcarrier spacing in the legacy preamble part and HE-SIG-A may be usedin some fields of the HE compatible part 720. For this, an FFT with fourtimes as many points as the FFT of the legacy preamble part(hereinafter, a four times FFT), i.e., a 256 FFT on the 20 MHz basicbandwidth, may be used. In this case, subcarrier spacing is 78.125kHz(=20 MHz/256). Accordingly, 256 subcarriers per symbol can be used onthe 20 MHz basic bandwidth. In this case, each symbol has a datainterval corresponding to an FFT period of 12.8 μs. Accordingly, alength of symbol duration excluding the GI from each symbol in some orall fields of the HE compatible part becomes four times a length ofsymbol duration excluding the GI from each symbol in the legacy preamblepart.

In one embodiment, the four times FFT of the legacy preamble part may beused in all fields of the HE compatible part 720 excluding the HE-SIG-Aand HE-STF. In another embodiment, an FFT having the same size as theFFT of the legacy preamble part may be used in the HE-SIG-B.

The GI has 0.4 μs length at 1/32 CP, has 0.8 μs length at 1/16 CP, has1.6 μs length at ⅛ CP, and has 3.2 μs length at ¼ CP. For example, whenthe ¼ CP is used, symbol duration is 16.0 μs. Accordingly, in the HEcompatible part, the symbol can be lengthened and the GI can belengthened on the same fractional CP basis, compared with the legacypreamble part.

A wireless communication network according to one embodiment may use anyone GI among the GIs shown in FIG. 10, FIG. 11, FIG. 12, and FIG. 13while using the 256 point FFT. A wireless communication networkaccording to another embodiment may use at least two GIs among the GIsshown in FIG. 10, FIG. 11, FIG. 12, and FIG. 13. In this case, thewireless communication network may select a GI in accordance with auser, or may select a GI in accordance with a channel or networkinterference.

In some embodiments, a frame may include GI information indicating theselected GI duration or FFT size information indicating the selected FFTsize (or subcarrier spacing information). In one embodiment, a signalfield (for example, a HE-SIG-A shown in FIG. 7 or a HE-SIG-B (notshown)) of the frame may include the GI information or the FFT sizeinformation (or subcarrier spacing information). In another embodiment,a MAC header of a MAC frame included in a data field of the frame mayinclude the GI information or the FFT size information (or subcarrierspacing information). The MAC frame may be a data frame, a controlframe, or a management frame. A transmitting device can notify areceiving device of the length of the used GI duration or the used FFTsize (or the used subcarrier spacing) through the GI information or theFFT size information (or the subcarrier spacing information). Thereceiving device can identify the length of the used GI duration or theused FFT size (or subcarrier spacing) through the GI information or theFFT size information (or the subcarrier spacing information) included inthe frame.

If the 0.4 μs GI is used in the 256 point FFT, the average throughputcan be improved by the short GI. For example, the average throughput maybe improved by 21% by a 0.4 μs GI compared with the 3.2 μs GI. However,the short GI may be vulnerable in the outdoor environment. If the 0.8 μsGI is used, the average throughput can be improved by 17% compared withthe 3.2 μs GI, but the performance can be degraded in the outdoorenvironment. The 1.6 μs GI may be fit for the outdoor environment, butmay provide less than average throughput enhancement. The 3.2 μs GI maybe best fit for the outdoor environment, but may provide no averagethroughput enhancement.

Therefore, in some embodiments, the 0.4 μs GI or 0.8 μs GI, i.e., 1/32CP or 1/16 CP, may be used to enhance the average throughput, and the1.6 μs GI or 3.2 μs GI, i.e., ⅛ CP or ¼ CP, may be used for outdoorrobustness.

A set of CPs allowed for the symbol having the subcarrier spacing of78.125 kHz may include 1/32 CP, 1/16 CP, ⅛ CP, and ¼ CP. In oneembodiment, 1/32 CP may be excluded from the allowed set of CPs.

Particularly, when a field indicating the GI information has 1 bit, theGI information of 1 bit cannot represent which CP is used from amongthree or more CPs. Accordingly, in one embodiment, two CPs among theabove four CPs may allowed for indoor transmission, and two CPs amongthe above four CPs may be allowed for outdoor transmission. Further, theset of CPs allowed for the indoor transmission may be different from theset of CPs allowed for the outdoor transmission. For example, in anembodiment, the set of CPs allowed for the indoor transmission mayinclude 1/16 CP and ⅛ CP, and the set of CPs allowed for the outdoortransmission may include ⅛ CP and ¼ CP.

In some embodiments, the signaling information may include anindoor/outdoor indication indicating the indoor transmission or theoutdoor transmission. The indoor/outdoor indication may have 1 bit. Inone embodiment, the signaling information may be transmitted through theHE-SIG-A.

In this case, a receiving device can identify the currently used CPbased on a combination of a transmission scheme indicated by theindoor/outdoor indication and the GI information. For example, when theindoor/outdoor indication indicates indoor transmission and the GIinformation is set to 1, 1/16 CP may be indicated between 1/16 CP and ⅛CP. When the indoor/outdoor indication indicates indoor transmission andthe GI information is set to 0, ⅛ CP may be indicated between 1/16 CPand ⅛ CP. Further, when the indoor/outdoor indication indicates outdoortransmission and the GI information is set to 1, ⅛ CP may be indicatedbetween ⅛ CP and ¼ CP. When the indoor/outdoor indication indicatesoutdoor transmission and the GI information is set to 0, ¼ CP may beindicated between ⅛ CP and ¼ CP.

In some embodiments, the indoor/outdoor indication may be transmittedthrough a bit that is not used in the frame in the previous WLAN.

As such, the frame whose symbol is lengthened may be appropriate for usein the outdoor environment. However, as described above, the frame mayinclude a plurality of long training fields (HE-LTFs) for the MIMOchannel estimation. In this case, when a length of each of the pluralityof HE-LTFs is increased by four times, the overhead may be increased bythe HE-LTFs. Hereinafter, an embodiment for reducing the length of theHE-LTF is described.

FIG. 14 illustrates general subcarrier allocation in a wirelesscommunication network according to an embodiment, FIG. 15 illustratessubcarrier allocation of a HE long training field in a wirelesscommunication network according to an embodiment, and FIG. 16illustrates generation of a HE long training field in a wirelesscommunication network according to an embodiment.

As shown in FIG. 14, a symbol in a frequency domain may be disposed on aplurality of subcarriers. When a 256 point FFT is applied to a 20 MHzbandwidth, the symbol may be disposed on 256 subcarriers. When the 20MHz bandwidth is divided into a plurality of subbands and the 256 FFT isapplied to the 5 MHz subband, the symbol may be disposed on 64subcarriers. When the 256 FFT is applied to the 10 MHz subband, thesymbol may be disposed on 128 subcarriers.

A center subcarrier among the plurality of subcarriers may be used as aDC (direct current) tone. An index of the center subcarrier used as theDC tone is 0. Some subcarriers that are disposed on both sides of the DCtone whose index is 0 may be also used as DC tones. Some subcarriersthat are disposed on both ends from the DC tone ins the center may beused as guard tones. Remaining subcarriers that exclude the DC tones andthe guard tones from entire subcarriers may be used as data tones. Whenpilots are transmitted, some of the data tones may be used as pilottones for transmitting the pilots.

Referring to FIG. 15, in one embodiment, values for a HE long trainingfield (HE-LTF), for example, non-zero values, may be allocated toeven-numbered subcarriers and zeros, i.e., null values, may be allocatedto odd-numbered subcarriers, among a plurality of subcarriers in theHE-LTF. That is, the values for the HE-LTF may be allocated to toneswhose indices are [±2, ±4, ±6, . . . ], and zeros may be allocated totones whose indices are [±1, ±3, ±5, . . . ]. In another embodiment, thevalues for the HE-LTF may be allocated to the odd-numbered subcarriersand zeros may be allocated to the even-numbered subcarriers. Some of theodd-numbered subcarriers or of the even-numbered subcarriers may not beused, instead may be used for DC tones or guard tones. As such, when aninverse Fourier transformer (140 of FIG. 2) performs an inverse Fouriertransform, for example an IFFT, after the values are allocated to thesubcarriers, a waveform of 12.8 μs length where a waveform of 6.4 μslength (excluding the GI) is repeated twice is output. That is, awaveform having a 6.4 μs period is output in two periods per symbol. Inan embodiment, only one period is transmitted as the HE-LTF among thetwo periods per symbol.

As such, although the four times FFT is used, the length of symbolduration excluding the GI from each symbol of the HE-LTF can be twicethe length of the symbol duration excluding the GI from each symbol ofthe legacy preamble part. Accordingly, the overhead by the HT-LTF can bereduced.

In one embodiment, since the length of the symbol duration excluding theGI from each symbol of the HE-LTF is 6.4 μs but the 256 FFT is appliedto the LTF on the 20 MHz basic bandwidth, subcarrier spacing in 256subcarriers may be 78.125 kHz.

In another embodiment, since the zeros, i.e., null values, are insertedinto the odd-numbered subcarriers among 256 subcarriers, it can beinterpreted that only the even-numbered subcarriers exist in the HE-LTFamong the 256 subcarriers. In an embodiment where only the even-numberedsubcarriers exist in the HE-LTF, the subcarrier spacing may be 156.25kHz, which is twice of 78.125 kHz.

In yet another embodiment, when the length of the symbol durationexcluding the GI from each symbol is 6.4 μs and the subcarrier spacingis 156.25 kHz(=20 MHz/128) in the HE-LTF, two times FFT of the legacypreamble part, i.e., a 128 point FFT on the 20 MHz basic bandwidth, maybe applied to the HE-LTF.

In some embodiments, the GI prepended to each symbol of the HE-LTF maybe selected from a set including 0.4 μs, 0.8 μs, 1.6 μs, and 3.2 μs. Inone embodiment, 0.4 μs may be excluded from the set. In one embodiment,the GI may be selected as any one of 1.6 μs and 3.2 μs to fit to theoutdoor environment. For example, the GI may be 3.2 μs. In this case,each symbol of the HE-LTF has 9.6 μs length. Alternatively, when thelength of the GI is 1.6 μs, each symbol of the HE-LTF has 8.0 μs length.

In some embodiments, since the four times FFT is used in some fieldsincluding a data field of the HE compatible part, a length of symbolduration excluding a GI from each symbol is 12.8 μs. The GI prepended toeach symbol may be selected from a set including 0.4 μs, 0.8 μs, 1.6 μs,and 3.2 μs. In one embodiment, 0.4 μs may be excluded from the set. Inone embodiment, the GI may be selected as any one of 1.6 μs and 3.2 μsto fit to the outdoor environment. For example, the GI may be 3.2 μs. Inthis case, each symbol of the data field has 16.0 μs length.

In some embodiments, an FFT having the same size as the legacy preamblepart may be applied to a HE short training field (HE-STF), for automaticgain control. Therefore, the HE-STF may have subcarrier spacing of 312.5kHz, and a length of symbol duration excluding the GI may be 3.2 μs.When ¼ CP is used, a GI may be 0.8 μs. In another embodiment, the HE-STFmay be generated in the manner described for the HE-LTF relative to FIG.15 such that a length of symbol duration excluding a GI from a symbol ofthe HE-STF is twice a length of symbol duration excluding the GI fromthe symbol of the legacy preamble part. That is, the 256 point FFT maybe applied to the HE-STF on the 20 MHz basic bandwidth, and the HE-STFmay use only one period of two periods that are output by allocatingvalues to only even-numbered (or, in another embodiment, odd-numbered)subcarriers among a plurality of subcarriers. The length of symbolduration excluding the GI may be 6.4 μs and the GI may have 1.6 μslength in a case of ¼ CP. That is, a length of the entire symbolduration is 8.0 μs. In a case that the GI has 3.2 μs length, the lengthof the entire symbol duration in the HE-STF may be 9.6 μs.

Next, various frame formats in a wireless communication networkaccording to an embodiment are described.

FIG. 17, FIG. 18, FIG. 21, and FIG. 22 each illustrates a frame formatin a wireless communication network according to various embodiments,and FIG. 19 and FIG. 20 show examples of subcarrier allocation in aframe format shown in FIG. 17. It is assumed in FIG. 17, FIG. 18, FIG.20, and FIG. 21 that a basic bandwidth, e.g., a 20 MHz bandwidth, isdivided into four subbands of, e.g., 5 MHz.

Referring to FIG. 17, a frame includes a legacy preamble part and a HEcompatible part. The legacy preamble part includes a legacy shorttraining field (L-STF), a legacy long training field (L-LTF), and alegacy signal field (L-SIG). The HE compatible part includes a HE signalfield (HE-SIG-A), a HE short training field (HE-STF), a HE long trainingfield (HE-LTF), an additional HE signal field (HE-SIG-B), an additionalHE long training field (HE-LTF), and a data field.

When the basic bandwidth is divided into a plurality of subbands, aplurality of subbands may be allocated to a plurality of devices.

For the compatibility with the previous WLAN, the L-STF, the L-LTF, andthe L-SIG of the legacy preamble part and the HE-SIG-A of the HEcompatible part are not transmitted on each subband but are transmittedby being encoded by a basic bandwidth unit, e.g., the 20 MHz band unit.In some embodiments, the HE-SIG-B may be also transmitted by beingencoded by the 20 MHz band unit. Further, the HE-STF used for theautomatic gain control may be also transmitted by being encoded by the20 MHz band unit.

The data field may be transmitted by being encoded by the subband unit,and a data field transmitted by being encoded by the subband unit mayinclude data for an allocated device. When lengths of data transmittedon the plurality of subbands are different, pad bits may be added to thedata field of the subband having the short data lengths such that thelengths of data transmitted on the plurality of subbands are the same.

In some embodiments, the HE-LTFs may include the first HE-LTF that istransmitted on the 20 MHz band without being divided into the pluralityof subbands and the additional HE-LTF that is transmitted on eachsubband. The number of HE-LTFs transmitted on each subband may bedetermined based on the number of data streams, i.e., space-time streamstransmitted on the corresponding subband. In the example shown in FIG.17, the number of HE-LTFs for the first subband (including the HE-LTFtransmitted by being encoded by the 20 MHz band unit) is four, thenumber of HE-LTFs for the second subband is one, and the number ofHE-LTFs for the third and fourth subbands is two. The HE-LTFs for eachsubband correspond to the first HE-LTF and the additional HE-LTFtransmitted on the corresponding subband. The HE-LTFs of each subbandmay have a predetermined pattern, and the predetermined pattern may beset to guarantee orthogonality among the plurality of subbands.

In some embodiments, the number of HE-LTFs may be the same for all ofthe subbands. That is, as shown in FIG. 18, the number of HE-LTFs forother subbands may be determined according to the number of HE-LTFs fora subband having the greatest number of space-time streams.

The HE-SIG-A may carry common signaling information. The HE-SIG-B maycarry allocation information for the subbands. That is, the HE-SIG-B mayinclude information representing which device is allocated to eachsubband. Accordingly, a device receiving a frame may identify a subbandallocated to the device from the HE-SIG-B and may interpret the HE-LTFand the data field of the allocated subband. The HE-SIG-B may furtherinclude information on occupancy time of each subband.

In some embodiments, the HE-SIG-B may further include information on thenumber of space-time streams at the MIMO transmission for each subband.The number of HE-LTFs may be determined based on the number ofspace-time streams. The HE-SIG-B may further include schedulinginformation indicating whether a multi-user MIMO (MU-MIMO) scheme isused. The number of bits for information to be carried by the HE-SIG-Bis increased as the number of subbands is increased. Accordingly, thenumber of bits included the HE-SIG-B may be flexibly adjusted byseparating the HE-SIG-B from the HE-SIG-A.

In one embodiment, the HE-SIG-B may follow the first HE-LTF as shown inFIG. 17. In another embodiment, the HE-SIG-B may follow the HE-SIG-A. Inthis case, the additional HE-LTF may follow the first HE-LTF.

In some embodiments, the frame may further include an additional HEsignal field (HE-SIG-C) transmitted on each subband. Accordingly, adevice receiving the frame can interpret only the HE-SIG-C of theallocated subband. The HE-SIG-C may include information on a modulationand coding scheme (MCS) used in the corresponding subband andinformation on a data size of the corresponding subband. When theMU-MIMO is applied to the subband, the HE-SIG-C may include the MCSinformation and the data size information for each device to which theMU-MIMO is applied. The HE-SIG-C may further include a cyclic redundancycheck (CRC). In an embodiment, the CRC may be calculated for a CRC checkon the corresponding subband. Alternatively, the CRC may be calculatedfor the CRC check on all of the subbands in order to reduce the totalnumber of CRC bits.

It is assumed in FIG. 17 that the first 5 MHz subband is allocated toone device (for example, device 0), the second 5 MHz subband isallocated to another device (for example, device 1), and 10 MHz of thethird and fourth subbands is allocated to yet another device (forexample, device 2). Since the third subband and the fourth subband areallocated to the same device, the additional HE-LTF, the HE-SIG-C, andthe data field of the third subband may be duplicated to the fourthband.

In the legacy preamble part and the HE-SIG-A, the 64 point FFT isapplied on the 20 MHz basic bandwidth and the GI of 0.8 μs is attachedto each symbol, like the previous WLAN. Accordingly, each of the L-STFand the L-LTF uses two symbols and has a length of 8 μs. The L-SIG usesone symbol and has a length of 4 μs. The HE-SIG-A may use two symbolslike an HT signal field (HT-SIG) of the HT WLAN or a VHT signal field(VHT-SIG-A) of the VHT WLAN. In this case, the HE-SIG-A has a length of8 μs.

The four times FFT is applied to the some fields in the HE compatiblepart excluding the HE-SIG-A. In one embodiment, the FFT of the legacypreamble part may be applied to the HE-STF for the automatic gaincontrol, and the four times FFT may be applied to remaining fields. Itis assumed that ¼ CP is used as the GI in all of these fields.

Then, the HE-STF of one symbol has a length of 4 μs, and each symbol ofthe HE-LTFs has a length of 16 μs. Further, each of the HE-SIG-B and theHE-SIG-C has a length of 16 μs when using one symbol.

As such, the frame shown in FIG. 17 or FIG. 18 can be suitably used inthe outdoor environment because the lengths of the symbol and the GI areincreased in some fields of the HE compatible part.

Referring to FIG. 19, the first HE-LTF and the HE-SIG-B transmitted onentire subbands use subcarriers from the 20 MHz bandwidth excludingsubcarriers used as DC tones and subcarriers used as guard tones. Pilottones may be allocated to some of the subcarriers of the first HE-LTFand the HE-SIG-B. FIG. 19 shows an example in which eight pilot tonesare allocated.

In the additional HE-LTF, the HE-SIG-C, and the data field that aretransmitted for each subband, subcarriers may be allocated for eachuser. Pilot tones may be allocated to some of the subcarriers.

In some embodiments, such as shown in FIG. 20, a guard band may beformed between the subbands allocated to the different users. That is,some subcarriers may be used as guard tones. Since the third and fourthsubbands (subbands 2 and 3) are allocated to the same user, the guardbands may be formed between the first and second subbands (subbands 0and 1) and between the second and third subbands (subbands 1 and 2), butno guard band may be formed between the third and fourth subbands(subbands 2 and 3), as shown in FIG. 20.

A frame where the guard band is formed between the subbands allocated tothe different users may be adapted for use in an uplink transmission.

According to embodiments illustrated in FIG. 17 and FIG. 18, becauselengths of the plurality of HE-LTFs included in the frame are increasedby a factor of four, the overhead may be increased by the HE-LTFs.Therefore, in another embodiment, as shown in FIG. 21, values for theHE-LTF, for example non-zero values, may be allocated to even-numberedsubcarriers and zeros may be allocated to odd-numbered subcarriers,among a plurality of subcarriers in the HE-LTF. That is, the values forthe HE-LTF may be allocated to tones whose indices are [±2, ±4, ±6, . .. ], and zeros may be allocated to tones whose indices are [±1, ±3, ±5,. . . ]. In another embodiment, the values for the HE-LTF may beallocated to the odd-numbered subcarriers and zeros may be allocated tothe even-numbered subcarriers.

As such, when an inverse Fourier transformer (140 of FIG. 2) performs aninverse Fourier transform, for example an IFFT, after the values areallocated to the subcarriers, a waveform of 12.8 μs length wherein awaveform of 6.4 μs length is repeated twice is output. That is, awaveform having a 6.4 μs period is output within two periods per symbol.Only one period is transmitted as the HE-LTF among the two periods persymbol. Then, a length of symbol duration excluding a GI is 6.4 μs inthe HE-LTF. If ¼ CP is used, the GI has a 1.6 μs length and the lengthof the entire symbol duration is 8.0 μs. Alternatively, if the GI has a1.6 μs length as shown in FIG. 21, the length of the entire symbolduration is 9.6 μs.

In one embodiment, since the length of the symbol duration excluding theGI from each symbol of the HE-LTF is 6.4 μs but the 256 FFT is appliedto the HE-LTF on the 20 MHz basic bandwidth, subcarrier spacing in 256subcarriers may be 78.125 kHz.

In another embodiment, since the zeros, i.e., null values, are insertedinto the odd-numbered subcarriers among 256 subcarriers, it can beinterpreted that only the even-numbered subcarriers exist in the HE-LTFamong the 256 subcarriers. In an embodiment where only the even-numberedsubcarriers exist in the HE-LTF, the subcarrier spacing may be 156.25kHz, which is twice of 78.125 kHz.

In yet another embodiment, when the length of the symbol durationexcluding the GI from each symbol is 6.4 μs and the subcarrier spacingis 156.25 kHz in the HE-LTF, two times FFT of the legacy preamble part,i.e., a 128 point FFT on the 20 MHz basic bandwidth, may be applied tothe HE-LTF.

As such, the length of symbol duration excluding the GI from each symbolof the HE-LTF is reduced by half compared with FIG. 17 and FIG. 18.Accordingly, the overhead of the HE-LTF can be decreased.

While a case modifying the frame described with reference to FIG. 17 hasbeen illustrated in FIG. 21, the frame described with reference to FIG.18 may be modified in the same way.

As shown in FIG. 22, a frame may be transmitted in an uplinktransmission as illustrated in FIG. 17, FIG. 18, and FIG. 21. FIG. 22illustrates an embodiment in which a frame illustrated in FIG. 21 isused for the uplink transmission.

For example, when device 0 is allocated the first subband, device 0 maytransmit the L-STF, the L-LTF, the L-SIG, the HE-SIG-A, the HE-STF, thefirst HE-LTF, and the HE-SIG-B through the 20 MHz band, and may transmitthe additional HE-LTF and the data field through the first subband.

While the frame transmission on the 20 MHz bandwidth has been describedabove, a frame according to an embodiment may be applied to a 20 MHz ormore bandwidth. For example, in some embodiments, a 40 MHz bandwidthtransmission, a 60 MHz bandwidth transmission, or an 80 MHz bandwidthtransmission may be performed by combining the 20 MHz bandwidths.Hereinafter, such embodiments are described with reference to FIG. 23and FIG. 24.

FIG. 23 and FIG. 24 schematically illustrating a frame format in awireless communication network according to various embodiments. It isassumed that an entire bandwidth is 40 MHz in FIG. 23 and an entirebandwidth is 80 MHz in FIG. 24.

Referring to FIG. 23, a frame includes a legacy preamble part for eachband having a basic bandwidth (for example, 20 MHz). In this case, alegacy short training field (L-STF), a legacy long training field(L-LTF), a legacy signal field (L-SIG), and a HE signal field (HE-SIG-A)of one 20 MHz band are duplicated to the other 20 MHz band.

A HE short training field (HE-STF), a HE long training field (HE-LTF),and an additional HE signal field (HE-SIG-B) of a HE compatible part maybe transmitted on the entire bandwidth (for example, 40 MHz).Alternatively, the HE-STF, the HE-LTF, and the HE-SIG-B may betransmitted on each 20 MHz. In this case, the HE-STF, the HE-LTF, andthe HE-SIG-B of one 20 MHz band are duplicated to the other 20 MHz band.

An additional HE long training field (HT-LTF), an additional HE signalfield (HE-SIG-C), and a data field are transmitted on each subband. Itis assumed in FIG. 23 that each 20 MHz band is divided into four 5 MHzsubbands.

As describe above, the four times FFT may applied to some fields of theHE compatible part, for example the HE compatible part excluding theHE-SIG-A and the HE-STF. In some embodiments, the HE-LTF may use onlyeven-numbered subcarriers.

As such, when a 256 FFT is applied on the 20 MHz basic bandwidth, thatis, when 256 subcarriers are used on the 20 MHz basic bandwidth, aproblem may occur when a VHT device detects a mid-packet.

The VHT WLAN uses a multi-channel by using secondary channels togetherwith a primary channel. That is, the VHT WLAN uses the primary channelof 20 MHz for a 20 MHz bandwidth transmission, uses the primary channelof 20 MHz and a secondary channel of 20 MHz for a 40 MHz bandwidth, anduses the primary channel of 20 MHz, the secondary channel of 20 MHz, anda secondary channel of 40 MHz for an 80 MHz bandwidth transmission.

The VHT device may detect whether a transmission from a neighbor BSS isa transmission that does not occupy its primary channel and occupies itssecondary channel. This detection is called a mid-packet detection. TheVHT device uses the mid-packet detection for clear channel assessment(CCA) of the secondary channel. In this case, the VHT device may performthe mid-packet detection on the secondary channel by receiving the frameshown in FIG. 23. However, in the frame shown in FIG. 23, a symbollength of the HE compatible part is different from a symbol length byrecognized the VHT device, i.e., a symbol length used in the VHT WLAN.Therefore, the GI that is used for the mid-packet detection by the VHTdevice cannot be a repetition of an end in an OFDM symbol. As a result,a problem may occur at the mid-packet detection by the VHT device, sothe compatibility with the VHT device may not be maintained.

Since the mid-packet detection is performed on the secondary channel, insome embodiments, the frame format that increases the symbol length insome or all fields of the HE compatible part may be used when only the20 MHz band of the primary channel is used, that is, when the secondarychannels are not used, in order to maintain the compatibility with theVHT device within the same BSS. Accordingly, the frame format thatincreases the symbol length in some or all fields of the HE compatiblepart may not be used when a transmission is performed through bandsincluding the secondary channel, so that compatibility with the VHTdevice can be maintained.

For example, a frame may be transmitted through an 80 MHz band as shownin FIG. 24. The frame includes a legacy preamble part for each bandhaving a basic bandwidth (for example, 20 MHz). In this case, a legacyshort training field (L-STF), a legacy long training field (L-LTF), alegacy signal field (L-SIG), and a HE signal field (HE-SIG-A) of one 20MHz band are duplicated to the other 20 MHz bands.

A HE short training field (HE-STF), a HE long training field (HE-LTF),and an additional HE signal field (HE-SIG-B) of a HE compatible part maybe transmitted on the entire bandwidth (for example, 80 MHz). In anotherembodiment, the HE-STF, the HE-LTF, and the HE-SIG-B may be transmittedon each 20 MHz band. In this case, the HE-STF, the HE-LTF, and theHE-SIG-B of one 20 MHz band are duplicated to the other 20 MHz bands.

An additional HE long training field (HT-LTF), an additional HE signalfield (HE-SIG-C), and a data field are transmitted on each subband. Inthe example shown in FIG. 24 the 80 MHz bandwidth is divided into four20 MHz subbands.

Since the 80 MHz bandwidth includes a secondary channel, a 64 point FFTmay be applied to all fields of the frame on the 20 MHz basic bandwidthfor compatibility with the VHT device. It is assumed in FIG. 24 that thenumber of symbols is four in the HE-SIG-B.

Embodiments of the WLAN supports backward compatibility with a previousversion device. Accordingly, frames of various formats may be usedwithin a BSS. In this case, a HE device may detect whether the receivedframe is a legacy frame, an HT frame, a VHT frame, or an HT frame usinga long OFDM symbol according to an embodiment. For this, anauto-detection scheme for detecting a frame format based on modulationschemes may be used.

Hereinafter, an auto-detection method in a wireless communicationnetwork according to an embodiment is described with reference to FIG.25 to FIG. 30.

FIG. 25 illustrates an auto-detection method of a legacy frame, FIG. 26illustrates an auto-detection method of an HT frame, FIG. 27 illustratesan auto-detection method of a VHT frame, and FIG. 28, FIG. 29, and FIG.30 each illustrates an auto-detection method of a HE frame in a wirelesscommunication network according to an embodiment.

As shown in FIG. 25, in a legacy frame, a symbol of a legacy signalfield (L-SIG) is modulated by using a binary phase shift keying (BPSK)modulation, and a data field following the L-SIG is modulated by usingvarious modulation schemes ranging from the BPSK modulation to a64-point quadrature amplitude modulation (64-QAM). As shown in FIG. 26,in an HT frame, an HT signal field (HT-SIG) having two symbols followsthe L-SIG modulated using the BPSK modulation. The two symbols of theHT-SIG are modulated using a quadrature binary phase shift keying(QBPSK) modulation having a different phase from the BPSK. As shown inFIG. 27, in a VHT frame, a VHT signal field (VHT-SIG-A) having twosymbols follows the L-SIG modulated by using the BPSK modulation. Thefirst symbol of the VHT-SIG-A is modulated by using the BPSK modulationand the second symbol of the VHT-SIG-A is modulated by using the QBPSKmodulation.

Accordingly, a HE device may determine that the received frame is the HTframe when the first symbol following the L-SIG is modulated by usingthe QBPSK modulation, and may determine that the received frame is theVHT frame when the first symbol following the L-SIG is modulated byusing the BPSK modulation and the second symbol is modulated by usingthe QBPSK modulation.

Referring to FIG. 28, according to one embodiment, in a HE frame, all ofa symbol of the L-SIG and two symbols of a HE signal field (HE-SIG-A)following the L-SIG are modulated by using the BPSK modulation. Further,a symbol following the two symbols of the HE-SIG-A, for example a HEshort training field (HE-STF), is modulated by using the QBPSK.

In another embodiment, the HE-STF may apply a 256 point FFT and use onlyeven-numbered subcarriers such as was described above for a HE longtraining field (HE-LTF). As a result, a length of the HE-STF may betwice that of a symbol of the legacy preamble part. In this case, asshown in FIG. 29, the HE-STF corresponding to the length of two symbolsmay be modulated by using the QBPSK modulation.

In yet another embodiment, as shown in FIG. 30, a symbol following twosymbols of the HE-SIG-A may be the third symbol of the HE-SIG-A. In thiscase, the third symbol of the HE-SIG-A may be modulated by using theQBPSK modulation.

Accordingly, the HE device may determine that the received frame is theHE frame when the first and second symbols following the L-SIG aremodulated by using the BPSK modulation and the third symbol is modulatedby using the QBPSK modulation.

As such, according to an embodiment, the HE device can automaticallydetect the frame format based on a combination of the BSPK and QBPSKmodulations.

Next, a frame transmitting method and a frame receiving method in awireless communication network according to an embodiment are describedwith reference to FIG. 31 and FIG. 32.

FIG. 31 is a flowchart illustrating a frame transmitting method in awireless communication network according to an embodiment, and FIG. 32is a flowchart illustrating a frame receiving method in a wirelesscommunication network according to an embodiment.

Referring to FIG. 31, a transmitting device generates symbols of alegacy preamble part and a HE signal field (HE-SIG-A) (S3110). Thetransmitting device performs an inverse Fourier transform to allow eachsymbol of the legacy preamble part and the HE-SIG-A to have subcarrierspacing of 312.5 kHz and a length of symbol duration (i.e., OFDM symbolduration) excluding a GI from each symbol to be 3.2 μs. A 64 point FFTmay be applied to the inverse Fourier transform on a 20 MHz basicbandwidth.

The transmitting device generates a HE long training field (HE-LTF) of aHE compatible part (S3120). In one embodiment, the transmitting deviceperforms the inverse Fourier transform to allow a symbol of the HE-LTFto have subcarrier spacing of 78.125 kHz, null values to be insertedinto odd-numbered subcarriers, and a length of symbol duration excludinga GI from the symbol of the HE-LTF to be 6.4 μs. In this case, thetransmitting device may perform the inverse Fourier transform by usingonly even-numbered subcarriers among a plurality of subcarriers, and maygenerate the symbol of the HE-LTF by using only one period of twoperiods that are output by the inverse Fourier transform. A 256 pointFFT may be applied to the inverse Fourier transform on the 20 MHz basicbandwidth.

In another embodiment, because the odd-numbered subcarriers into whichthe null values are inserted can be interpreted as non-existingsubcarriers, the transmitting device may perform the inverse Fouriertransform to allow the symbol of the HE-LTF to have subcarrier spacingof 156.25 kHz and the length of OFDM symbol duration excluding the GI tobe 6.4 μs. In this case, the transmitting device may perform the inverseFourier transform on the HE-LTF by applying a 128 point FFT on the 20MHz basic bandwidth.

The transmitting device generates a data field of the HE compatible part(S3130). The transmitting device performs the inverse Fourier transformto allow a symbol of the data field to have subcarrier spacing of 78.125kHz and a length of symbol duration excluding a GI from the symbol to be12.8 μs. The 256 point FFT may be applied to the inverse Fouriertransform on the 20 MHz basic bandwidth.

In one embodiment, the transmitting device may perform the inverseFourier transform to allow a symbol of the HE-STF to have subcarrierspacing of 312.5 kHz and a length of symbol duration excluding a GI fromthe symbol of the HE-STF to be 3.2 μs.

In another embodiment, the transmitting device may perform the inverseFourier transform to allow the symbol of the HE-STF to have subcarrierspacing of 78.125 kHz and the length of symbol duration excluding the GIfrom the symbol of the HE-STF to be 6.4 μs.

In yet another embodiment, the transmitting device may perform theinverse Fourier transform to allow the symbol of the HE-STF to havesubcarrier spacing of 78.125 kHz and the length of symbol durationexcluding the GI from the symbol of the HE-STF to be 12.8 μs.

In one embodiment, the transmitting device may perform the inverseFourier transform to allow a symbol of an additional HE signal field(HE-SIG-B) to have subcarrier spacing of 312.5 kHz and a length of aninterval excluding a GI from the symbol of the HE-SIG-B to be 3.2 μs.

In another embodiment, the transmitting device may perform the inverseFourier transform to allow the symbol of the HE-SIG-B to have subcarrierspacing of 78.125 kHz and the length of symbol duration excluding the GIfrom the symbol of the HE-SIG-B to be 12.8 μs.

Next, the transmitting device transmits a frame including the legacypreamble part and the HE compatible part (S3140).

While the steps S3110, S3120, and S3130 have been sequentially shown inFIG. 31, the steps S3110, S3120, and S3130 may be performed in adifferent order. Alternatively, at least two steps of the steps S3110,S3120, and S3130 may be performed at the same time.

Referring to FIG. 32, a receiving device in a frame including a legacypreamble part and a HE compatible part detects symbols of the legacypreamble part and the HE compatible part (S3210). Each symbol of thelegacy preamble part and the HE signal field (HE-SIG-A) has subcarrierspacing of 312.5 kHz and a length of an interval excluding a GI fromeach symbol is 3.2 μs.

In an embodiment, a symbol of a HE long training field (HE-LTF) in theHE compatible part has subcarrier spacing of 78.125 kHz, null values areinserted into odd-numbered subcarriers in the symbol of the HE-LTF, anda length of symbol duration excluding a GI from the symbol of the HE-LTFis 6.4 μs.

In another embodiment, the symbol of the HE-LTF may have subcarrierspacing of 156.25 kHz and the length of symbol duration excluding the GImay be 6.4 μs. A symbol of a data field in the HE compatible part hassubcarrier spacing of 78.125 kHz and a length of symbol durationexcluding a GI from the symbol is 12.8 μs.

In one embodiment, a symbol of a HE short training field (HE-STF) in theHE compatible part may have subcarrier spacing of 312.5 kHz and a lengthof symbol duration excluding a GI from the symbol of the HE-STF may be3.2 μs.

In another embodiment, the symbol of the HE-STF may have subcarrierspacing of 78.125 kHz and the length of symbol duration excluding the GIfrom the symbol of the HE-STF may be 6.4 μs.

In yet another embodiment, the symbol of the HE-STF may have subcarrierspacing of 78.125 kHz and the length of symbol duration excluding the GIfrom the symbol of the HE-STF may be 12.8 μs.

In one embodiment, a symbol of an additional HE signal field (HE-SIG-B)in the HE compatible part may have subcarrier spacing of 312.5 kHz and alength of symbol duration excluding a GI from the symbol of the HE-SIG-Bmay be 3.2 μs.

In another embodiment, the symbol of the HE-SIG-B may have subcarrierspacing of 78.125 kHz and the length of symbol duration excluding the GIfrom the symbol of the HE-STF may be 12.8 μs.

The receiving device processes the symbols in the received frame (S3220,S3230, and S3240).

In some embodiments, the receiving device performs a Fourier transformon the symbol of the legacy preamble part (S3220). A 64 point FFT may beapplied to the Fourier transform on the 20 MHz basic bandwidth.

The receiving device performs a Fourier transform on the symbol of theHE-LTF of the HE compatible part (S3230). In one embodiment, thereceiving device may, at the time of Fourier transform, copy an intervalexcluding a GI from the symbol of the HE-LTF, i.e., the interval havinga length of 6.4 μs to generate an interval having two periods, and mayapply a 256 point FFT to the interval having two periods on the 20 MHzbasic bandwidth.

In another embodiment, the receiving device may, at the time of Fouriertransform, apply a 128 point FFT to a symbol of the HE-LTF on the 20 MHzbasic bandwidth.

The receiving device performs a Fourier transform on a symbol of a datafield of the HE compatible part (S3240). The receiving device may applythe 256 point FFT to the symbol of the data field on the 20 MHz basicbandwidth.

In one embodiment, the receiving device may apply the 64 point FFT to asymbol of the HE-STF on the 20 MHz basic bandwidth. In anotherembodiment, the receiving device may process the HE-STF in the same wayas the HE-LTF. In yet another embodiment, the receiving device may applythe 256 point FFT to the symbol of the HE-STF on the 20 MHz basicbandwidth.

In one embodiment, the receiving device may apply the 64 point FFT to asymbol of an additional HE signal field (HE-SIG-B) on the 20 MHz basicbandwidth. In another embodiment, the receiving device may apply the 256point FFT to the symbol of the HE-SIG-B on the 20 MHz basic bandwidth.

While the steps S3220, S3230, and S3240 have been sequentially shown inFIG. 32, the steps S3220, S3230, and S3240 may be performed in adifferent order. Alternatively, at least two steps of the steps S3220,S3230, and S3240 may be performed at the same time.

A frame transmitting method and a frame receiving method according toabove embodiments may be executed by a baseband processor 10 shown inFIG. 1 to FIG. 3. In one embodiment, instructions for executing theframe transmitting method and the frame receiving method according toabove embodiments may be stored in a non-transitory computer-readablerecording medium such as a memory 40. In another embodiment, at leastsome of the instructions may be MAC software. In yet another embodiment,at least some of the instructions may be transmitted from anon-transitory computer-readable recording medium of a certain serverand may be stored in the memory 40.

While this invention has been described in connection with what ispresently considered to be practical embodiments, it is to be understoodthat the invention is not limited to the disclosed embodiments, but, onthe contrary, is intended to cover various modifications and equivalentarrangements included within the spirit and scope of the appendedclaims. Further, two or more embodiments may be combined.

What is claimed is:
 1. A method of transmitting a frame by a device in a wireless communication network, the method comprising: generating a first symbol having a first subcarrier spacing, a symbol duration of the first symbol, excluding a guard interval, having a first length; generating a second symbol having a second subcarrier spacing narrower than the first subcarrier spacing, a symbol duration of the second symbol, excluding a guard interval, having a second length that is twice the first length; and transmitting a frame including the first symbol and the second symbol, wherein generating the second symbol includes: allocating non-zero values to even-numbered subcarriers of a plurality of subcarriers; allocating zero values to each of odd-numbered subcarriers of the plurality of subcarriers; generating a waveform by performing an inverse Fourier transform on the plurality of subcarriers, the waveform having a duration; and generating the second symbol using only half of the duration of the waveform.
 2. The method of claim 1, wherein the first length is 3.2 μs and the second length is 6.4 μs.
 3. The method of claim 1, further comprising generating a third symbol, a symbol duration of the third symbol, excluding a guard interval, having a third length that is twice the second length, wherein the frame further includes the third symbol.
 4. The method of claim 3, wherein the third length is 12.8 μs.
 5. The method of claim 3, wherein the frame includes a legacy preamble part, a HE (high efficiency) long training field that is adapted for use in channel estimation, and a data field, and wherein the legacy preamble part includes the first symbol, the HE long training field includes the second symbol, and the data field includes the third symbol.
 6. The method of claim 5, wherein a basic bandwidth of the frame is divided into a plurality of subbands, wherein the data field is encoded per each subband and transmitted, and wherein the data field transmitted on the subband includes data for a receiving device allocated to the subband.
 7. The method of claim 6, wherein the frame further includes a first HE signal field and a second HE signal field that both follow the legacy preamble part, and wherein the second HE signal field is encoded per the basic bandwidth and transmitted, and includes allocation information of the subbands.
 8. The method of claim 7, wherein the second HE signal field further includes information on devices that receive the frame on each subband.
 9. The method of claim 6, wherein the basic bandwidth is 20 MHz.
 10. The method of claim 5, wherein the legacy preamble part further includes a legacy signal field, and wherein two symbols that immediately follow the legacy signal field are modulated by using BPSK (binary phase shift keying) modulation.
 11. The method of claim 1, wherein generating the second symbol further includes allocating a zero value to even-numbered subcarriers used for Direct Current (DC) tones of the plurality of subcarriers.
 12. The method of claim 1, wherein a first half of the waveform is identical to a second half of the waveform.
 13. A method of receiving a frame by a device in a wireless communication network, the method comprising: detecting in a frame a first symbol having a first subcarrier spacing, a symbol duration of the first symbol, excluding a guard interval, having a first length; detecting in the frame a second symbol having a second subcarrier spacing narrower than the first subcarrier spacing, a symbol duration of the second symbol, excluding a guard interval, having a second length that is twice the first length; processing the first symbol in the frame; and processing the second symbol in the frame using a period, excluding a guard interval, of the second symbol, wherein processing the second symbol includes: generating a copy of the second symbol; generating an input of a Fourier transform, the input corresponding to two copies of the second symbol; and performing the Fourier transform, using a fast Fourier transform (FFT) having a first size, on the input.
 14. The method of claim 13, wherein processing the first symbol in the frame includes: performing a Fourier transform on the first symbol by using an FFT having a second size different from the first size, wherein the first size is four times the second size.
 15. The method of claim 13, wherein the first length is 3.2 μs and the second length is 6.4 μs.
 16. The method of claim 13, wherein the frame further includes a third symbol, a symbol duration of the third symbol, excluding a guard interval, having a third length that is twice the second length.
 17. The method of claim 16, wherein the frame includes a legacy preamble part, a long training field that follows the legacy preamble part and is adapted for use for channel estimation, and a data field, and wherein the legacy preamble part includes the first symbol, the long training field includes the second symbol, and the data field includes the third symbol.
 18. The method of claim 17, wherein the frame further includes a first HE signal field and a second HE signal field that both follow the legacy preamble part, wherein a basic bandwidth of the frame is divided into a plurality of subbands, and the data field is encoded per a subband unit and transmitted on a subband of the plurality of subbands, and wherein the second HE signal field is encoded per the basic bandwidth and transmitted, and includes allocation information for the subbands.
 19. The method of claim 18, wherein the second HE signal field further includes information on devices that receive the frame on each subband.
 20. The method of claim 17, wherein the legacy preamble part further includes a legacy signal field, and wherein two symbols that immediately follow the legacy signal field are modulated by using BPSK (binary phase shift keying) modulation. 